The research of CMOS device gate engineering with the “high-K gate dielectric/metal gate” as the core technique is a most typical key process in the techniques of 22 nm node and below, and researches on materials, processes, and structures associated therewith are widely carried out. Currently, researches on the high-K gate dielectric/metal gate technique may be generally divided into the gate-first process where a gate is formed before formation of the source and drain and the gate replacement process where a gate is formed after formation of the source and drain, in which process the gate need not to experience high annealing temperature.
For the gate-last process, a very important process is filling of high-K gate dielectrics and metal gate materials in the gate groove. With continuous reduction in the feature size of a MOS device, particularly when it enters into 22 nm and below technical nodes, the physical gate length of a MOS device has been reduced to 30 nm below, and meanwhile the height of the gate shall also be kept at a certain level (e.g., about 30 nm) so as to reduce the gate resistance. However, great difficulty exists when filling various materials in such a nano-scale gate groove with an aspect ratio larger than 1. Typical difficulties lie in the uniformity of the metal gate layer and high-K gate dielectric layer in the gate groove as well as the holes in the filled metal. The holes in the filled metal appear mainly due to an intrinsic phenomenon of Step Coverage during thin film deposition. Although we could overcome the Step Coverage by optimizing deposition methods and improving deposition conditions, optimizing the gate structure and reducing the aspect ratio of the gate groove shall be a more efficient solution in terms of the filling capability for a narrow trench.
So, there exists a need for a semiconductor device based on gate replacement technology and a method for manufacturing the same, which can both reduce the aspect ratio of a gate groove and ensure a sufficiently low gate resistance.